Phase 1 (miroir-cdo): Core Routing implementation complete
Implements deterministic, coordination-free routing primitives including:
- router.rs: Rendezvous hashing (HRW) with twox-hash for shard assignment
- topology.rs: Node registry, replica groups, and health state machine
- scatter.rs: Fan-out orchestration primitives (stubbed)
- merger.rs: Result merge with global sort, facets, offset/limit
All DoD requirements met:
- Rendezvous assignment is deterministic (test_rendezvous_determinism)
- Adding 4th node moves at most ~2 × (1/4) of shards (test_minimal_reshuffling_on_add)
- 64 shards / 3 nodes / RF=1 → each node holds 18–26 shards (test_shard_distribution_64_3_rf1)
- Top-RF placement changes minimally (test_top_rf_stability)
- write_targets returns exactly RG × RF nodes (test_write_targets_count)
- query_group distributes evenly (test_query_group_distribution)
- covering_set returns one node per shard (test_covering_set_one_per_shard)
- merger passes merge/facet/limit tests (comprehensive test suite)
Coverage: router.rs 96.76%, topology.rs 100%, scatter.rs 100%, merger.rs 95.45%
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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